It is sometimes necessary to provide a vapour compression system in which two or more evaporators are fluidly connected in parallel between a compressor and a common outlet. This is, e.g., the case in many refrigeration systems comprising two or more separate refrigeration compartments, e.g. household refrigerators having a chilling compartment and a freezing compartment. Alternatively, two or more evaporators may be arranged in the same refrigerated volume, e.g. in a side by side configuration. An example of such a construction could be an air condition system. When two or more evaporators are fluidly coupled in parallel in this manner, a distribution of the available refrigerant between the evaporators must be obtained. It is desirable that the distribution takes various individual factors of the evaporators into consideration. Such individual factors may include individual set point temperatures, refrigeration load, efficiency, etc.
Various attempts to obtain a desired distribution of refrigerant in one of the vapour compression systems defined above have been tried. Thus, DE 195 47 744 discloses a refrigeration system comprising a compressor and two evaporators fluidly coupled in parallel to the compressor. The flow of refrigerant across both evaporators is controlled by means of an electrically controlled magnet valve. The valve is controlled on the basis of measurements of temperatures inside two separate compartments, each being refrigerated by one of the evaporators. Thus, the valve is controlled in such a manner that each evaporator receives a correct amount of refrigerant to obtain a proper hysteresis control of the corresponding refrigeration compartment. A disadvantage of this control method is that it requires a separate temperature sensor for each evaporator. Another disadvantage is that it can not be ensured that the potential refrigeration capacity of each evaporator is utilised to the greatest possible extent. Yet another disadvantage is that it is not suitable for use in a system where the evaporators are arranged in the same refrigerated volume, e.g. in an air condition system.
U.S. Pat. No. 6,546,843 discloses a machine for producing and dispensing cold or iced beverages comprising a plurality of beverage-containing tanks. Each tank is provided with an evaporator for a refrigerating circuit and a mixer. The evaporators are connected with one and the same compressor by connection and controlled shutoff valves. Flow of refrigerant to each of the evaporators is controlled on the basis of a measured temperature in each of the tanks. Valves controlling fluid flows to the individual evaporators may be controlled sequentially. It is necessary to position a temperature sensor in each of the tanks, and the other disadvantages described above are also present in this machine.